wkt@csadfa.cs.adfa.oz.au (Warren Toomey) (06/05/91)
After recompling a program under SunOS 4.1.1 I found that it doesn't run
the same way any more. I understand that 4.1.1 now has POSIX job control,
but I can't see why this would affect non-POSIX job control code. A
small program that reproduces the `bug' is included below. It runs under
Pyramid OSx and Ultrix, but not SunOS 4.1.1. I'd be very grateful for any
ideas, especially if it's a problem with my code.
For those who have already seen this in another newsgroup, sorry, the
reponse I got was NULL. Feel free to flame as much as you like :-)
Warren Toomey
wkt@csadfa.cs.adfa.oz.au
#!/bin/sh
echo x - fred.c
sed '/^X/s///' > fred.c << '/'
X#include <signal.h>
X#include <sgtty.h>
X#include <termio.h> /* Need this for TCGETA definition */
X
X
X/* The following program exhibits a possible bug in SunOS 4.1.1. Compile
X * this program as fred: cc -o fred fred.c and run it with no arguments.
X *
X * The program sets the terminal to stop background writes to the terminal,
X * and forks a child. The child moves itself to a new process group, and
X * tries to write to the terminal in one of two ways: just after the fork(),
X * and after the exec().
X *
X * The parent waits for the SIGCHLD caused by the write, and attempts to
X * bring the child back into the parent's pgrp, thus allowing the write to
X * succeed.
X *
X * However, this fails under SunOS 4.1.1 when the child only tries to write
X * AFTER the exec(). See `THE BUG' comment below.
X */
X
Xvoid catchsig()
X { }
X
Xvoid dowrite()
X { write(1,"Writing to stdout\n",18); exit(0); }
X
X
Xmain(argc,argv)
X int argc;
X char *argv[];
X {
X struct termio tbuf;
X int i;
X
X if (argc>1) dowrite(); /* If we are called with >1 args, write */
X
X/* Set up the terminal so that SIGTTOUs are sent to
X * processes which are not members of the owning process group
X */
X if (ioctl(0,TCGETA,&tbuf)) perror("ioctl in settou");
X tbuf.c_lflag |= TOSTOP;
X if (ioctl(0,TCSETA,&tbuf)) perror("ioctl s");
X
X
X/* Catch the SIGCHLD with a null handler.
X */
X signal(SIGCHLD,catchsig);
X
X/* Fork, and make the child write on stdout.
X */
X switch(i=fork())
X {
X case -1: printf("Could not fork\n"); exit(1);
X
X case 0 : /* The child */
X
X i=setpgrp(0,getpid()); /* Take us out of the pgrp */
X sleep(2); /* Wait for a bit */
X
X/* THE BUG:
X *
X * If you uncomment the printf line, the program works everywhere.
X * But if you leave the line commented, the program dies with an
X * EPERM error in the parent's setpgrp() under SunOS Release 4.1.1.
X * It works under Pyramid OSx, generic 4.3BSD system.
X */
X /* printf("Can I write??\n"); */
X execlp("fred","arg1","arg2",0);
X exit(0);
X
X default: /* The parent */
X
X printf("Forked, now we pause()\n");
X pause(); /* Wait for SIGCHLD */
X if (setpgrp(i,getpgrp(0))==-1) /* set pgrp to the parents's */
X { perror("Setpgrp failed"); exit(1); }
X kill(i,SIGCONT); /* Start the child up */
X sleep(1); /* and finish */
X exit(0);
X }
X }
/